(Photo by Elisa Kagan) Full size image available here |
A new method for dating destructive past earthquakes, based on evidence remaining in caves has been developed by scientists at the Hebrew University of Jerusalem and the Geological Survey of Israel.
Using this method, they discovered for the first time evidence of earthquakes that can be documented some distance from the Syrian-African rift that runs from Syria through Lebanon, Israel and Jordan and down into Africa. This rift caused great shifts in the topography of the region in prehistoric times.
An article on this subject was published this month in the journal Geology. The article is based on work carried out by graduate student Elisa J. Kagan of the Institute of Earth Sciences at the Hebrew University and on a report issued by the Geological Survey of Israel, a government research body.
Stalactite caves retain a record of environmental conditions, including climate and the seepage of water through cracks in the earth. The researchers examined the stalactite cave near Beit Shemesh and another nearby cave, which are located about 40 kilometers west of the Dead Sea. The Dead Sea itself is part of the Syrian-African rift.
The researchers estimate that there were at least 13 earthquakes of a magnitude of 7.5 or greater on the Richter Scale that occurred in the region in the last 200,000 years. However, in the two caves that were examined there was no evidence of an earthquake of such magnitude in the last 4,000 years. The scientists suggest, therefore, that the prehistoric earthquakes that hit the region (during the time of the great Syrian-African rift upheavals) were of greater magnitude than those recorded later.
Together with her advisor, Prof. Amotz Agnon of the Hebrew University Institute of Earth Sciences, Kagan further noted the patterns of fallen stalactites and stalagmites in the caves and found that they had fallen primarily in the direction of north to south and east to west. The researchers showed through calculations that these patterns were caused by extremely large earthquakes that originated in the Dead Sea Region.
In her research, Kagan examined those stalactites and stalagmites upon which new stalagmites had grown, indicating passage of many thousands of years. In the dating of this material, she was guided by Dr. Miryam Bar-Matthews and Dr. Avner Ayalon of the Geological Survey of Israel.
The scientists are continuing their investigative work in the caves in connection with Kagan's doctoral research.